The levels of recovery of Steptococcus mutans from clinical specimens vary depending on the isolation medium used. The purpose of this study was to determine the relative recoveries of S. mutans on 10 isolation media, and to see whether any of the serotypes are selectively inhibited by any of the media tested. Results show that the choice of an isolation medium will have a definite influence on the number of S. mutans colonies observed. Furthermore, it was demonstrated some individual serotypes are selected against by certain isolation media.